The retina and pigment epithelium are neuroepithelial tissues that work in close cooperation, as do other ocular tissues. Specific growth and differentiating factors found in the eye guide the development and interactions of individual ocular tissues to form a functional visual system. For example, ocular tissues synthesize insulin-like growth factor (IGF-I) and its binding proteins (BP), thus may self-regulate activity of this important growth factor in the vitreous and surrounding tissues. In addition to IGFBP, we have identified a unique differentiating protein secreted from fetal human pigment epithelial cells called pigment-epithelial-derived factor that is neurotropic to cultured human retinoblastoma cells and may affect neural retinal development in vivo. This protein maps to chromosome 17p where there is a cluster of cancer-related genes.